A charging device for a motor vehicle is also referred to as an on-board charger (a charger on board). A similar charging device can be coupled with a charging cable for transmission of one-phase or multi-phase alternating voltage, for example through a charging socket. The charging device will then convert the alternating voltage into a direct voltage by means of which the high-voltage battery of the motor vehicle can be charged.
A motor vehicle charging device must also provide fault current protection. In particular, an all-current sensitive DC vault current detection (DC—direct current) of less than 6 milliamperes is prescribed according to IEC 62752 for charging of motor vehicles in order to safely prevent DC fault current residual current feedback of high voltage batteries in supply networks external to the vehicle. The required DC fault current detection is usually carried out with a fault current detector FI of type B, which must be provided in the three-phase current or AC voltage connection of the charging station. This means that providing such loading stations is cost-intensive.
German Patent Application No. DE 10 2011 118 716 A1 discloses a storage system for electrical energy, which is provided with a positive connection and with a negative connection, wherein protection is provided respectively to interrupt a charging current and a discharging current, and wherein in addition, a semiconductor switch is provided for bidirectional blocking. A flyback diode can be connected in parallel to the semiconductor switch to prevent overvoltage when inductivity is switched on.
German Patent No. DE 296 08 208 U1 discloses a battery charger that is provided with a constant current control circuit, in with which thyristors are connected in series to an electrical coil and generate, from alternating voltage, a DC charging current in cooperation with the coil.
German Patent Application No. DE 10 2011 006 096 A1 discloses a charging control system that is equipped with a first connecting device for connecting a charging cable of an external charging station located outside the motor vehicle, and with a second connection device for connecting a high voltage battery. For safe disconnection of the high voltage battery from the first connection device of the charging cable, a mechanical switch is provided both in the positive line and in the ground line of the charging device for galvanic interruption of the electrical connection.